PULLING UP TROUBLE CODES AND WON'T RUN UP, I

I need to know how to pull up trouble codes-my check engine light is on. The engine will start and run and after a bit, the idle runs down to under 800 rpm, then, if you try to throttle up, it stumbles and pops in the intake snoot. If I spray a little starting fluid in the snoot while opening the throttle, it will run up as normal. Important note. I just got this car back from the repair shop a month ago, the check engine light was on when we got it back. They replaced the fuel pump, the fuel pump relay, the cold start relay, and the engine computer behind the right kick panel inside the car. It also has a new crankshaft sensor in it as well. The air filter is not the problem, I ruled that out by removing the snoot at the air cleaner box and performance was the same. Help!